Question: Which of these numbers is prime? ${32,\ 33,\ 39,\ 67,\ 93}$
Answer: A prime number has exactly two factors: 1 and itself. The factors of 32 are 1, 2, 4, 8, 16, and 32. The factors of 33 are 1, 3, 11, and 33. The factors of 39 are 1, 3, 13, and 39. The factors of 67 are 1 and 67. The factors of 93 are 1, 3, 31, and 93. Thus, 67 is a prime number.